1. Field of the Invention
The present invention relates generally to an organic EL (electroluminescent) device using an organic compound. More specifically, this invention is concerned with a simulation method and system for providing an organic EL device that enable the light emitted therefrom to be effectively available with a reduced emission luminance variation, and an organic EL device as well.
2. Discussion of the Background
In recent years, organic EL devices have been under intensive investigation. One such device is basically built up of a thin film form of hole transporting material such as triphenyldiamine (TPD) deposited by evaporation on a hole injecting electrode, a light emitting layer of fluorescent material such as an aluminum quinolinol complex (Alq.sup.3) laminated thereon, and a metal (electron injecting) electrode of a metal having a low work function such as Mg and formed on the light emitting layer. This organic EL device now attracts attention because a very high luminance ranging from several hundred to tens of thousand cd/m.sup.2 can be achieved with a voltage of approximately 10 V.
The organic EL device has a basic arrangement including on a substrate a film form of organic EL structure comprising an electron injecting electrode, an organic layer, a hole injecting electrode, etc., as mentioned just above. Usually, the light emitted from the device is taken out of the substrate side via the hole injecting electrode.
Regarding an organic EL device in general, it is known that emission spectra of light emitting species are modulated by optical interference in the device, upon which they leave the device. For this reason, even when an organic EL device comprising the same light emitting material is applied to a different optical system, there are changes in the spectra emitted out of the device, and their intensity.
The greatest optical modulation is known to occur by interference between forwardly emitted light and light emitted backwardly and reflected at a metal surface (electron infecting electrode), as set forth in JP-A 4-328295. This effect is expressed in terms of a function determined by a distance between a light emitting point and the metal surface, and so an optical arrangement for obtaining the desired modulated spectra can be known therefrom. However, this is still less than satisfactory for making much more precise estimations, for the reason of large errors. In other words, another parameter for consideration is required.
In this regard, JP-A 7-240277 reveals another problem, i.e., the modulation of light emitted out of an organic EL device due to interference of light reflected at an interface between glass and a transparent electrode. However, the publication merely states that to increase the intensity of emitted light of a specific wavelength in a narrow range by making use of optical modulation, it is only required to regulate an optical thickness between the glass/transparent conductive film interface and a metal surface with an organic multilayer structure interleaved between them to a specific value.
Here assume a certain optical system. Then, it would be difficult to make any detailed study of spectral modulation without expectation of to what degree the spectra are modulated by interference caused by a parameter other than the aforesaid one. This would in turn make the optical design of an optimized device difficult. In the prior art, the influence of a more sophisticated arrangement, for instance, an arrangement comprising many reflective interfaces in addition to the interface between the organic multilayer structure and the transparent conductive film is not taken into account. Nor is the utilization of such an arrangement investigated.